Gas distributor for casting mold manufacture

ABSTRACT

A gas distributor for use in a mold cup and main sprue of a casting mold to be coated internally with a pyrolytic coating includes a gas receiving and distributing nozzle and a main sprue conduit. The nozzle delivers gas to the cup through a plurality of discharge holes and the conduit delivers gas to the base of the main sprue. Hole outlets deliver such gas angularly along the cup toward the main sprue to avoid turbulent flow.

United States Patent 1191 11 1 3,731,650

Schweikert et al. 1 May 8, 1973 54 GAS DISTRIBUTOR FOR CASTING 1,356,71510/1920 l-lachmann ..1 18/48 x MOLD MANUFACTURE 2,586,348 2/1952 Kuebler..118/48 lnveaiais'ywimar '11. schwe'iiea; "3611'; s.

Me o 9 Gin/@93 6 Qh Q Assignee: General Electric Company, Cincinnati,Ohio Filed: Nov. 3, 1971 Appl. No.: 195,284

u.s. c1 ..118/48, 239/543 111:. c1 ..C23 l 3 0 FieldofSearch T118/47-49.5; 117/106- 107.2; 239/539, 543

References Cited UNITED STATES PATENTS 3/1920 Hachmann ..l l8/48 XPrimary Examiner-Morris Kaplan Attorney-Derek P. Lawrence et a1.

[57 ABSTRACT A gas distributor for use in a mold cup and main sprue of acasting mold to be coated internally with a pyrolytic coating includes agas receiving and distributing nozzle and a main sprue conduit. Thenozzle delivers gas to the cup through a plurality of discharge holesand the conduit delivers gas to the base of the main sprue. Hole outletsdeliver such gas angularly along the cup toward the main sprue to avoidturbulent flow.

1 Claim, 1 Drawing Figure PAIENIEBH 3,731,650

INVENTORSJ 6'41 FZWV ,WILBUR H. SCHWEIKERT JOMN S. MOSIER ,4 770EMEY-GAS DISTRIBUTOR FOR CASTING MOLD MANUFACTURE BACKGROUND OF THE INVENTIONThe high chemical reactivity between molten metals found in Group IV bof the Periodic Table of Elements with refractory material generallyused in precision casting molds has resulted in the use of suchmaterials as graphite as a mold material or as a barrier material withinthe mold. One method for making a mold suitable for use in casting oftitanium articles involves the deposition of a pyrolytic coating, oneexample of which is graphite, on the inner walls of such a mold. Suchpyrolytic graphite coating method and the resulting mold is described inU.S. Pat. No. 3,284,862 Schweikert, issued Nov. 15, 1966 and assigned tothe assignee of the present invention.

One problem which has been recognized in the manufacture of such a moldis the proper introduction and application of a gas from which thepyrolytic coating is produced. Such gas is first introduced on walls ofthe pouring cup and main sprue which first receive molten metal and onwhich a heavier coating generally is necessary because of washing by themolten metal. In one example, under certain conditions, it was foundthat either blistering of pyrolytic graphite occurred in such areas orpyrolytic graphite was not properly formed due to turbulent gas flow orregions of gas stag nation.

SUMMARY OF THE INVENTION It is a principal object of the presentinvention to provide, for use in the apparatus for providing a pyrolyticcoating on internal walls of a casting mold, a gas distributor for themold cup and main sprue to avoid turbulent flow and gas stagnation inthose areas during generation of the pyrolytic coating.

Another object is to provide apparatus including such a distributor tohold both the distributor and the mold during processing.

These and other objects and advantages will be more clearly understoodfrom the following detailed description, the examples and the drawing,all of which are meant to be representative of rather than limiting onthe scope of the present invention.

Briefly, the present invention, in one form, provides, in apparatus forproviding a pyrolytic coating on internal walls of the casting mold, agas distributor for use in a mold cup and main sprue connected with thecup. The gas distributor comprises a gas receiving and distributingnozzle and a main sprue conduit. The gas receiving and distributingnozzle includes a gas inlet and a conduit port which communicates with aconduit inlet. Also included is a nozzle wall, the outer surface ofwhich is shaped generally to conform with the shape of the cup and whichconverges toward the main sprue conduit. Through the nozzle wall are aplurality of gas discharge holes the outlets of which direct the gasangularly along the cup in the direction of the main sprue in order toavoid turbulent flow and gas stagnation.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a sectional, partiallydiagrammatic view of the gas distributor of the present inventionpositioned within a casting mold for provision of a pyrolytic coating onthe internal walls of the mold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Precision casting molds ofrefractory materials have long been produced by the well knowninvestment casting technique sometimes referred to as the lost waxprocess. For the manufacture of precision cast parts, such as those madeof Ti or its alloys, it has been recognized that the interposition ofcertain pyrolytic coatings between the refractory material and the metalto be cast into the mold avoids reaction between the mold and the metal.In addition, use of a pyrolytic coating reduces contamination of themetal with coating material.

In practical casting manufacture, such precision casting molds are madeto produce a plurality of articles in a single mold. Such a moldincludes a pouring cup into which molten metal is first poured. Themolten metal then passes into a main sprue or passageway from which itis passed into various other secondary passages which feed molten metalto that portion of the mold which is to produce the article. Thus, it isimportant that the pouring cup and main sprue be able to withstandwashing of the molten metal in order to avoid reaction with therefractory material of which the mold walls are made.

It has been found that the present invention, positioned in the drawingin use in the generation of a pyrolytic coating on the walls of aprecision casting ceramic mold, avoids the problems of coatingblistering and powdering such as sooting in the case of pyrolyticgraphite. In the drawing, the gas distributor of the present inventionincludes a gas receiving and distributing nozzle shown generally at 10and preferably of graphite and a main sprue conduit shown generally at12 and preferably of ceramic material such as dense aluminum oxide. Thegas receiving and distributing nozzle has a gas inlet 14 and a conduitport 16 communicating with conduit inlet 18. The gas receiving anddistributing nozzle 10 also includes a nozzle wall 20 having an outersurface 22 shaped generally to conform with the shape of mold pouringcup 24 and converging generally toward conduit port 16. A plurality ofgas discharge holes 28 extend through nozzle wall 20. Each dischargehole has a hole outlet 30 which directs gas entering nozzle 10 throughgas inlet 14 angularly toward the main sprue conduit 12 and along thecup in the direction of the main sprue 26.

The main sprue conduit 12 communicates with the gas receiving anddistributing nozzle 10 at the distributing nozzle 's conduit port 16 andthe main sprue conduit inlet 18. Gas received by the main sprue conduitis discharged through conduit outlet 32 generally toward main sprue base34, thus avoiding gas stagnation in that region.

Gas discharged from the gas distributor of the present invention throughgas discharge hole outlets 30 is directed in substantially laminar flowby outlets 30 along with surface of mold pouring cup 24 toward and intothe interior of main sprue 26, toward main sprue base 34. In the area ofthe main sprue base, it mingles with gas discharged from conduit outlet32 for distribution into other portions of the mold upon the walls ofwhich the pyrolytic coating is to be deposited. For example, gas passesthrough secondary channels 36 into article mold cavity 38 in which theprecision cast article is to be produced. The gas then is dischargedthrough mold vents 40.

During processing of the mold to deposit a pyrolytic coating on itsinner walls, the mold is placed in an ordinary heating enclosure (notshown), which can discharge gas emitted from mold vents 40. One suchenclosure is shown in the above identified U.S. Pat. No. 3,284,862 as agraphite susceptor enclosing the mold. Surrounding the susceptor is aninduction coil which, together with the susceptor, serves as a means toheat the mold and the gas through radiation. A graphite cover and agraphite base, shown partially in the drawing at 41, can be used tocomplete the enclosure.

Although the entire heated enclosure is not shown because of the varietyof ways in which such heating can be accomplished, the drawing does showa graphite mold and nozzle holder 42 which rests within such'enclosureon base 41 and which is adapted to carry both the casting mold as wellas the gas distributor of the present invention. Mold pouring cup lip 44is located within holder first recess 46 to block gas discharged fromoutlets 30 from flowing around lip 44 and away from main sprue 26. Inaddition, nozzle wall rim portion 48 of nozzle wall 20 is located withinholder second recess 50 to position outer surface 22 of nozzle wall 20in proper spaced relationship with pouring cup 24. If desired, a sealingmaterial 52, commonly used in the art, can be located in recess 46 andbeneath holder 42 for additional sealing. Holder 42 includes a holdergas inlet 54 which cooperates with nozzle gas inlet 14 and base gasinlet 56 to allow passage of gas from a source, (not shown), into nozzle10.

In one example, a ceramic shell mold having porous walls was made fromcommercially available materials by the lost wax process. Afterdewaxing, the mold was mounted on holder 42 on which had been mountedthe gas distributor of the present invention, as shown in the drawing.The assembly thus provided was placed in a vacuum furnace apparatus, ofthe type described above, where it was heated in the range of l900 2200F. During that time, acetylene gas was introduced through inlets 54 and56 into gas inlet 14 of mold through vents 40. The result was acontinuous pyrolytic graphite coating on the internal walls of the moldwithout blistering or sooting on such critical surfaces as those of thepouring cup 24 and the main sprue base 34.

Thus, the present invention, which provides gas in laminar flow alongcritical internal wall surfaces of a mold on which a pyrolytic coatingis to be'deposited, avoids blistering and sooting through controlled gasflow and elimination of gas stagnation. Although the present inventionhas been described in connection with specific examples and embodiments,it will be understood by those skilled in the art, the modificationssuch as in conditions, materials, configurations, etc. and othervariations which can be made within the scope of the present invention.

What is claimed is:

1. In apparatus for providing a pyrolytic coating on internal walls of acasting mold through use of a gas, a gas distributor for use in a moldcup and main sprue connected with the cup, the gas distributorcomprising:

a gas receiving and distributin nozzle- D a mam sprue conduit open a aconduit mlet and a conduct outlet;

the gas receiving and distributing nozzle including:

a. a gas inlet;

b. a conduit port communicating with the conduit inlet;

c. a nozzle wall having an outer surface shaped generally to conformwith the shape of the cup and converging toward the conduit port; and

d. a plurality of gas discharge holes through the nozzle wall, eachhaving a hole outlet which directs the gas angularly toward the mainsprue conduit whereby gas is passed along the cup in the direction ofthe main sprue; and

a mold and nozzle holder including:

a. a holder first recess shaped to receive a mold pouring cup lip;

b. a holder second recess located radially inward from the holder firstrecess and shaped to receive the nozzle wall rim portion; and

c. the holder having a holder. gas inlet radially inward from the holdersecond recess.

4 18 I I it

1. In apparatus for providing a pyrolytic coating on internal walls of acasting mold through use of a gas, a gas distributor for use in a moldcup and main sprue connected with the cup, the gas distributorcomprising: a gas receiving and distributing nozzle; a main sprueconduit open at a conduit inlet and a conduct outlet; the gas receivingand distributing nozzle including: a. a gas inlet; b. a conduit portcommunicating with the conduit inlet; c. a nozzle wall having an outersurface shaped generally to conform with the shape of the cup andconverging toward the conduit port; and d. a plurality of gas dischargeholes through the nozzle wall, each having a hole outlet which directsthe gas angularly toward the main sprue conduit whereby gas is passedalong the cup in the direction of the main sprue; and a mold and nozzleholder including: a. a holder first recess shaped to receive a moldpouring cup lip; b. a holder second recess located radially inward fromthe holder first recess and shaped to receive the nozzle wall rimportion; and c. the holder having a holder gas inlet radially inwardfrom the holder second recess.